This application claims the priority of Korean Patent Application No. 10-2013-0020254, filed on Feb. 26, 2013, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference.
In general, demand for secondary batteries has been rapidly increased as technology development and demand with respect to mobile devices have increased. Among these secondary batteries, lithium (ion/polymer) secondary batteries having high energy density and operating voltage as well as excellent shelf-life and cycle life characteristics have been widely used as energy sources of various electronic products as well as various mobile devices.
A lithium secondary battery is typically composed of an electrode assembly that is formed by sequentially stacking electrodes and separators, and a case or pouch accommodating the electrode assembly and an electrolyte. Also, the electrode assembly is composed of a unit cell or a bi-cell as a major component.
Referring to Korean Patent Application Laid-Open Publication No. 2008-0095770, a bi-cell, in which a cathode, a separator, an anode, a separator, and a cathode, are sequentially stacked, and a bi-cell, in which an anode, a separator, a cathode, a separator, and an anode are sequentially stacked, are disclosed.
These bi-cells may be formed by alternatingly disposing an electrode (cathode or anode) and a separator, and attaching each layer to each other.
Typically, since binder layers are respectively formed on the surface of the electrode and the surface of the separator, the electrode and the separator are attached to each other when heat and pressure are applied to the electrode and the separator. Thus, the bi-cells may be formed using such a method.
The separator is mainly formed of a polymer material and has shrinkage properties due to heat. Therefore, the separator may be shrunk when heat is supplied from the outside of the secondary battery or heat is generated from the inside of the secondary battery, and as a result, there is a risk that a short circuit may occur due to the contact between the cathode and the anode.
In order to prevent the above phenomenon, a separator having a bigger size than an electrode is used in a bi-cell. However, when the bi-cell is formed using the above separator, edges of the separator may be maintained in the state in which the edges are not attached to the electrode, and typically, a series of processes of preparing a secondary battery may be continuously performed without a special treatment for the edges of the separator.
However, in order to securely prevent the short circuit of the separator, a separator having a considerably larger size than the electrode must be prepared, and as a result, the volume of the secondary battery may eventually increase.
Also, since the separator may be used more than necessary, manufacturing costs of the secondary battery may increase.